Finding lighter or “bleached” spots on underwear can be surprising, but it’s usually nothing to worry about. Many assume it comes from detergent or washing, but in most cases, “it’s usually a completely normal and harmless effect.”

The cause is natural vaginal discharge. This fluid helps clean the body by removing bacteria and dead cells, making it “a routine, healthy bodily function.” It plays an important role in maintaining balance and protecting the vaginal area.

The key factor is acidity. The vaginal environment has a slightly acidic pH that supports good bacteria and prevents harmful ones. When this discharge touches fabric, especially darker materials, the mild acidity can slowly fade the dye. Over time, this creates the “lighter or ‘bleached’ patches” people notice.

The effect isn’t the same for everyone. Body chemistry, hydration, amount of discharge, and even the type of fabric can all change how visible the marks become. Some may barely notice it, while others see more obvious discoloration.

In most cases, these marks are actually a good sign. They show the body is maintaining its natural balance and protection. However, changes in discharge should still be monitored. Unusual odor, color, itching, or discomfort may signal a problem and should be checked by a healthcare professional.